1. Field of the Invention
This present invention relates to a polymer membrane, and more particularly, to a chitosan membrane containing nano-inorganic particles and the method for forming the same.
2. Description of the Prior Art
Chitosan is a hydrophilic natural polymer, which has received much attention in recent years. Chitosan is a polysaccharide consisting of [(1,4)-2-amino-2-deoxy-β-D-glucan]. Usually, a deacetylation process is taken to produce chitosan from chitin. Chitin is also a natural polymer and consists of [(1,4)-2-acetamido-2-deoxy-β-D-glucan]. Chitin is the major constituent of the exoskeleton of insects and crustaceous aquatic animals, and also the major constituent of the cell wall of fungus. Chitosan is biodegradable and has the characteristics of excellent biocompatibility and almost no immunoreaction and no toxicity. Furthermore, because of the amino and hydroxyl groups in its molecular structure, chitosan is chemical reactive and is easy to be modified to from a variety of derivatives. For the above reasons, chitosan can be applied in many fields, such as: agriculture, medical and health care, food processing, fine chemicals, waste water treatment, and textile and paper-making industries.
Pervaporation is a membrane separation process that can be employed to separate liquid mixtures. It can be used to separate liquid mixtures with azeotrope. In addition, it comprises the advantages such as easy operation, energy saving, and others. Therefore, pervaporation attracts much attention in industry. The key of the development of pervaporation is the preparation of membranes with excellent separation performance. The separation mechanism is the difference in the penetration rate of each component in the feed to cross the membrane, and the permeation rate is determined by the solubility and the diffusivity of each component in the membrane. The diffusivity is related to the size of the molecule permeating through the membrane and the solubility is related to the affinity between the permeating molecules and the membrane. Thus, a strategy to improve pervaporation performance is to adjust the affinity between the preferred component and the membrane. For example, to synthesize a material with special hydrophilic property or to modify the commercial material for raising the hydrophilicity is practiced. Another application is to control the membrane structure for adjusting the diffusivity of the permeating components in the membrane. Because of its high hydrophilicity and good membrane-forming property, chitosan is a good material for preparation of pervaporations.
Chitosan can be prepared by a dry process, in which the chitosan/acid/water solution is evaporated to remove water and to form dense membranes. However, such membranes cannot be directly used in the pervaporation process because the chitosan membrane would re-dissolve when being in contact with aqueous solution, an effect caused by the residual acid in the membrane. Evan after the removal of the residual acid, the membrane would still be not stable when being applied to the pervaporation process, because of the swelling effect by the feed aqueous solution. Thus, a crosss-linking process is usually required. Sulfuric acid, aldehyde, and dialdehyde are common crosslinkers. After cross-linking, although the stability and permselectivuty are improved, the permeation flux is low (Uragami and Tadashi, U.S. Pat. No. 5,006,255), which limits the application of chitosan membranes to pervaporation. Therefore, a new process is still required to prepare chitosan membranes that posses high selectivity, high flux, and high stability for the pervaporation process.